1. Field of the Invention
This invention relates to a value selection mechanism, and more particularly to a postage value selection mechanism including a security device for preventing the printing of postage without payment being made and for easily detecting tampering of the postage value selection mechanism.
2. Description of the Related Art
U.S. Pat. No. 4,050,374 for a METER SETTING MECHANISM, issued Sep. 27, 1977 to Check, Jr. and assigned to the assignee of the present invention and incorporated by reference herein, discloses a mechanism for selecting postage values which are to be printed by a rotary postage meter. The drive shaft of the drum includes a plurality of selectable racks, each of which is slidably movable in engagement with a different pinion gear, connected to an associated print wheel within the drum, for selectively rotating the print wheel to dispose a printing element or font thereof at the outer periphery of the drum for printing purposes. The value selection mechanism includes a first stepper motor which is operable for selecting one of the racks, and a second stepper motor which is operable for actuating the selected rack for selectively rotating the desired printing element of the associated print wheel to the printing position thereof. An electronic control system (not shown) which is coupled to a keyboard for processing postage value entries made by an operator, selectively drives the respective stepper motors in response to keyboard entries.
U.S. Pat. No. 4,630,210 for a MICROPROCESSOR CONTROLLED D.C. MOTOR FOR CONTROLLING A LOAD, issued Dec. 16, 1986 to Salazar, et al., and assigned to the assignee of the present invention and incorporated by reference herein, shows a conventional postage meter including a plurality of lengthwise translatable racks mounted in channels formed in the drive shaft of a rotatable postage printing drum. The drum includes a plurality of print wheels, which are mounted for rotation in the drum, and a like number of pinion gears connected on a one-for-one-basis with an associated print wheel. Each of the pinion gears is disposed, on a one for one basis, in meshing engagement with each of the rack gears, so that lengthwise translation of a rack gear results in rotation of the associated print wheel to a selected position thereof wherein a printing font at the periphery of the print wheel is located for printing purposes when the drum is rotated.
U.S. Pat. No. 4,649,814, for ROTARY SELECTOR DEVICE, issued Mar. 17, 1987 to Sette and assigned to the assignee of the present invention and incorporated by reference herein, shows a rotary value selection mechanism, of the type used for selecting and driving the respective translatable racks of the aforesaid U.S. Pat. No. 4,630,210, including a first annularly-shaped rack selection member having a pinion gear mounted therewithin and movable therewith for selectively engaging the racks as the first member is rotated, and including a second annularly-shaped printwheel font selection member which is disposed in meshing engagement with the pinion gear teeth for translating the selected rack to move the associated print wheel as the second member is rotated.
U.S. Pat. No. 3,682,378 for VALUE DISPENSING MECHANISMS, issued Aug. 8, 1972 to Rouan, et al. and assigned to the assignee of the present invention and incorporated herein by reference, shows a value selection mechanism whereby the plurality of print wheels are movable via a mechanical gear/lever arrangement.
Value selection mechanisms of the aforesaid types have from time-to-time become physically damaged such that one or more rack gears have become disassociated from its associated print wheel driving gear, with the result that the print wheels may be rotated independently thereof. Whereupon, a postage value can be printed which is different from that which has been selected by the associated, translating, rack gear. Although the occurrence of such physical damage may be apparent to a postage meter user, meters have been known to be continued to be used despite such a malfunction condition, in order to wrongfully print postage values without a payment being made therefor. Of course, since postage meters are required to be physically inspected on a semi-annual basis, and more frequently based on mail volume and postage, such physical damage has a short life span if it is discovered during the inspection. Nevertheless, any postage payment losses are rightfully of great concern to the Postal Service and to postage meter manufacturers. As a result, a series of experimental activities with postage meters have been conducted to determine the basic cause, if any, of disassociation of postage selecting racks and print wheels. And, it has been experimentally determined that the instances in which such disassociation's occur are due to a sufficient force being exerted against the print wheel to separate the same from the drive train therefor. Such a force could, for example, occur if someone tried to force movement of the printwheel in an attempt to print postage values without a payment being paid therefrom.
U.S. Pat. No. 5,295,433 for A VALUE SELECTION MECHANISM INCLUDING MEANS FOR WEAKENING A SHAFT THEREOF, issued Mar. 22, 1994 and assigned to the assignee of the present invention is incorporated by reference herein and discloses a device which solves, to some degree, the problems of the prior art discussed above. U.S. Pat. No. 5,295,433 shows a shaft mounted in a printhead drum and upon which a first gear rack is slidably mounted, via supporting elements, to a pinion gear associated with a print wheel. When the first gear rack is driven along the shaft due to interaction with a second gear rack, the pinion gear is forced into rotation thereby rotating the print wheel to position the selected printing element into a print position. The shaft upon which the first gear rack slides includes a circumferentially extending channel therein which acts as a weakened portion of the shaft. Thus, when a force tending to disassociate the print wheel from the first gear rack is applied to the print wheel, the shaft will permanently bend at the channel in response to the force. When bending occurs, the supporting elements of the first gear rack can no longer freely slide along the shaft, thereby jamming the value selection mechanism.
Copending U.S. patent application No. 08/308,044, entitled VALUE SELECTION AND PRINTING APPARATUS INCLUDING A SECURITY DEVICE and filed on Sep. 16, 1994, discloses yet another device for preventing the printing of incorrect postage. This device utilizes a novel sleeve disposed around a weakened rack gear guide shaft which will jam when a force sufficient to disassociate the print wheel from the rack gear is exerted against the print wheel.
Copending U.S. patent application No. 08/085,382 filed Jul. 2, 1993 also discloses a security mechanism for a postage meter in which a rotatable drive gear deforms in response to a force applied thereto and thereby jams the printing mechanism.